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Fire ecology
Fire ecology

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4.1 Fire and ecological succession

Early successional communities establish themselves relatively quickly after a fire (rapid colonisers) while late successional communities establish themselves much later (Figure 21).

The diagram shows six stages of ecological succession starting on the left and proceeding to the right. Time is represented by a horizontal arrow from left to right. Each stage of succession is illustrated by a drawing of the type of vegetation that would be found at that stage. At the first stage there is bare rock, at the second stage there are mosses and grasses, at the third stage there are grasses and perennials, at the fourth stage woody pioneers are in evidence, at the fifth stage fast-growing trees have appeared; at the sixth and final stage there is a climax forest. Above the drawings of the six stages are a series of lines depicting the increase in abundance of habitat as the stages proceed so that at the first stage, bare rock predominates with no vegetation present. This is gradually replaced by mosses and grasses at stage 2 and then at stage 3 grasses and perennials appear, followed by woody plants, fast-growing trees and then larger trees. So, at stage 6 the climax forest consists of a complex mixture of vegetation.
Figure 21  Diagrammatic representation of forest succession over time. There is a steady increase in biodiversity, biomass and thickness of soil layer as succession proceeds, i.e. as time passes.

Although fires open up gaps for early successional communities, community composition – the number and diversity of species present – is profoundly affected by the fire regime, and in particular its frequency and/or intensity.

For example, if fires are frequent the community will be dominated by early-succession, opportunistic, fast-colonising, resistant species because species characterising later successional stages will not be able to become established before the next fire.

  • What kind of community would be expected if fires are rare?

  • The community tends to be dominated by a few highly competitive, late-succession species. These species outcompete earlier-colonising species and can become established before the next fire.